The demand for increased storage capacity in memory or rigid disks and the trend towards miniaturization of memory or rigid disks (due to the requirement for smaller hard drives in computer equipment) continues to emphasize the importance of the memory or rigid disk manufacturing process, including the planarization or polishing of such disks for ensuring maximal performance. Apart from their well-known use in notebook computers, hard disk drives are also found in car navigation systems and digital video cameras. The recording media for hard disk drives used in such mobile devices has to be able to prevent data loss, which means it must have the ability to withstand vibration and shock. Glass memory disks have superior shock-resistance characteristics in comparison to the aluminum disks that are used in non-portable equipment. As a result, there is an increased interest in the use of glass as a substrate in memory disk applications.
As the demand for increased storage capacity has increased, so has the need for improved processes for the polishing of such memory or rigid disks. The term “memory or rigid disk” refers to any magnetic disk, hard disk, rigid disk, or memory disk for retaining information in electromagnetic form. The memory or rigid disk typically has a surface that comprises nickel-phosphorus, but the memory or rigid disk surface can comprise any other suitable material. The planarity of the memory or rigid disks must be improved, as the distance between the recording head of a disk drive and the surface of the memory or rigid disk has decreased with improvements in recording density that demand a lower flying height of the magnetic head with respect to the memory or rigid disk. In order to permit a lower flying height of the magnetic head, improvements to the surface finish of the memory or rigid disk are required.
Along with the need to improve planarity of memory disks is a need to decrease the surface roughness of the disks and to reduce the number of microasperities found thereon. While there exist several chemical-mechanical polishing (CMP) compositions and methods for use in conjunction with metallic memory disks, few conventional CMP methods or commercially available CMP compositions are well-suited for the planarization or polishing of glass memory or rigid disks. Attempts have been made to decrease surface roughness by reducing the particle size of abrasives used in the polishing compositions; however, removal rates and therefore throughput can be drastically reduced with use of smaller abrasive particle size.
Thus, there remains in the art a need for improved polishing methods for the polishing of glass substrates.